The long term goal of this project is to develop a method of assessing the otolith organs suitable for a clinical vestibular laboratory. Current testing of patients with dizziness and disequilibrium focuses primarily on the evaluation of the horizontal semicircular canals; there is, in particular, no established method of clinically evaluating the otolith organs of the inner ear. Building upon previous work performed to date, this project will further develop off-vertical axis rotation (OVAR). OVAR was selected because of its ease of use and its ability to stimulate the otolith organs alone or in combination with the semicircular canals. Two of the specific aims of the work proposed herein are to correlate vestibulo-ocular response patterns with demonstrable vestibular pathology using OVAR. We will use two models of vestibular pathology, surgically confirmed unilateral peripheral vestibular lesions and lesions of the vestibulo-cerebellum; a control population will be tested for comparison. Two other specific aims are to investigate 1) the three dimensional eye movements (horizontal , vertical, and torsional) induced by constant velocity OVAR, and 2) the role of velocity storage in semicircular canal-otolith interaction. Stimuli will consist of computer-controlled earth-vertical axis rotation and OVAR using constant velocity and sinusoidal velocities. Eye movements will be measured with electrooculography and magnetic scleral search coils. Data will be recorded on a digital computer and processed with specialized software to quantitate response parameters. By testing several hypotheses, we expect that these studies will 1) lead to an improved understanding of the pathophysiology of otolith-ocular connections, 2) provide further insight into how OVAR testing fits into the current clinical battery of vestibular function tests, and 3) guide our thinking regarding how OVAR testing may be refined to answer specific questions regarding vestibulo-ocular function and dysfunction.